1. Field of the Invention
The present invention relates to a process for preparing a thin film of oxide superconductor on a single crystal substrate of semiconductor by physical vapour deposition.
2. Description of the related art
Superconducting oxide materials such as Y--Ba--Cu--O system, Bi--Sr--Ca--Cu--O system, T1--Ba--Ca--Cu--O system or the like are expected to be utilized in electronics devices such as Josephson element or superconducting transistors due to their high critical temperatures (Tc). In order to realize such electronics devices, it is indispensable to prepare thin films of these oxide superconductors.
Recently, it has become possible to prepare single crystal thin films of these oxide superconductors of good quality on a single crystal substrate of MgO, SrTiO.sub.3 or the like by physical vapour deposition technique including sputtering, vacuum evaporation and laser abrasion or by chemical vapour deposition technique.
However, in the case of the superconducting transistors in which a single crystal thin film of oxide superconductor must be deposited on a single crystal substrate of semiconductor, it is impossible or very difficult to prepare a thin film of oxide superconductor having good crystallinity. In fact, when an oxide superconducting material is deposited on a single crystal substrate of semiconductor such as a silicon single crystal, separated island portions of the oxide superconducting material which are separated from each other are formed initially on the substrate until a thin film of oxide superconducting material becomes to a thickness of about 200 .ANG.. Therefore, even if deposition of the oxide superconducting material is continued further on such separated islands of the oxide superconducting material, the resulting thin film can not be a uniform and smooth thin film having good crystallinity.
Although a uniform and smooth thin film of oxide superconductor may be obtained by lowering a substrate temperature during deposition, the thin film prepared at low temperatures is poor in crystallinity in such extent that the thin film can not be used in actual applications.
Therefore, an object of the present invention is to solve the problems and to provide a process for preparing a single crystal thin film of oxide superconductor of high quality on a single crystal substrate of semiconductor such as silicon.